H2: Absolute zero-carbon propulsion systems

氢是碳质燃料的一种有吸引力的替代品，有可能使航空航天应用的绝对零碳推进系统成为可能。用于发电的陆基燃气轮机已经成功地使用了通过预混燃料喷射器输送的氢气。虽然预混提供了最低的NOx排放，但它很容易闪回，现代航空航天燃气轮机的高温还存在自燃的风险。这些都是重大的安全问题，可以通过将氢直接喷入燃烧室以形成扩散火焰来解决。这种安排需要对空气动力运输过程进行仔细的塑造。必须确保再循环，以提供稳定性，并且需要高强度湍流以快速混合燃料/空气以控制局部化学计量比。微型混合装置通过在燃烧室周围分布小规模的燃料和空气喷射点来实现这一点。较小的尺寸必然导致高应变率、短混合时间和低停留时间，这是降低NOx的理想条件，但对可靠点火具有挑战性。此外，已经确定了微混合火焰合并的倾向，从而导致NOx排放增加。尽管这种行为主要归因于各个注入部位之间的间距，但对导致聚合的注入参数尚未进行详细研究。发展对这种行为的基本了解对航空航天应用至关重要，在航空航天应用中，需要更紧密的喷油器间距来最大化功率密度，从而最小化发动机重量。该项目将使用专门为高保真光学测量设计的新大气压力测试设备，通过实验建立控制航空兼容氢空气微混合喷射器性能的流动物理和燃烧过程。虽然对流动物理的理解的提高将对开发符合航空航天标准的氢燃料喷射系统具有重要价值，但这些发现还将与其他部门相关。氢气燃烧为清洁能源提供了机会，并具有广泛应用的潜力，例如传统的陆上发电、微型燃气轮机、工业、家庭和区域供暖系统。此外，生成的综合数据集将引起CFD社区的极大兴趣，为验证下一代建模工具提供有价值的数据。将进行广泛的测试活动，以建立微混合喷射燃烧性能以及定义这一点的流体传输过程的物理基础。高保真光学测量将应用于一系列几何图形，提供无与伦比的流动物理研究。关键的航空性能指标(点火、稳定性、排放、燃烧室出口温度分布)将通过混合行为与设计参数相关。这些科学发现将为未来的工业发展提供可靠的基础。这项研究的目的是为在航空中建立氢气燃烧提供科学依据。为了最大限度地发挥这项工作的影响，将制定一项引入微混合喷油器的最佳战略。在整个项目中获得的测量数据和理解将用于评估航天推进系统的特殊要求对微混合喷射系统设计的影响。

Hydrogen presents an attractive alternative to carbonaceous fuels, potentially enabling absolute zero carbon propulsion systems for aerospace applications. Land-based gas turbines for power generation have already demonstrated successful operation using hydrogen delivered through premixed fuel injectors. Whilst premixing offers the lowest NOx emissions, it is susceptible to flashback and the high temperatures in modern aerospace gas turbines additionally risk autoignition. These represent significant safety concerns which can be addressed by the direct injection of hydrogen into the combustion chamber to form a diffusion flame. This arrangement requires careful shaping of the aerodynamic transport processes. Recirculation must be ensured, to provide stability, and high intensity turbulence is required for rapid fuel/air mixing to control local stoichiometry. Micro-mix devices achieve this by distributing small scale fuel and air injection sites around the combustor. The small size inherently leads to high strain rates, short mixing timescales and low residence times, ideal conditions for reducing NOx, but challenging conditions for reliable ignition. Additionally, a propensity for micro-mix flames to coalesce has been identified, giving rise to increased NOx emissions. The injection parameters responsible for coalescence have not been studied in detail, although the behaviour has been attributed primarily to the spacing between individual injection sites. Developing fundamental understanding of this behaviour is crucial for aerospace applications, where tighter injector spacing is desirable to maximise power density and so minimise engine weight.This project will experimentally establish the flow physics and combustion processes controlling performance for aviation compliant hydrogen air micro-mix injectors using a new atmospheric pressure test facility, designed specifically for high-fidelity optical measurements. Whilst the improvement in understanding of the flow physics will be of significant value for the development of aerospace compliant hydrogen fuel injection systems, the findings will additionally be relevant to other sectors. Hydrogen combustion presents an opportunity for clean energy and has potential for wide application, for example conventional land-based power generation, micro-gas turbines, industrial, domestic and district heating systems. Additionally, the comprehensive data sets produced will be of significant interest to the CFD community, providing valuable data for validation of the next generation of modelling tools.An extensive test campaign will be performed to establish the micro-mix injection combustion performance as well as the physics underpinning the fluid transport processes defining this. High-fidelity optical measurements will be applied to a range of geometries, providing an unparalleled study of the flow physics. Key aerospace performance metrics (ignition, stability, emissions, combustor exit temperature profile) will be related to design parameters through the mixing behaviour. The scientific findings will provide secure foundations for future industrial development.The intention of the research is to provide the scientific basis for establishing hydrogen combustion within aviation. To maximise the impact from this work, an optimum strategy for the introduction of micro-mix injectors will be developed. Measurement data and understanding gained throughout the project will be used to evaluate the impact of aerospace propulsion system specific requirements on the design of micro-mix injection systems.